• CAC (Customer Acquisition Cost): Customer Acquisition Cost refers to the cost of getting customers to purchase a product or service.
• LTV (Customer Lifetime Value): Customer Lifetime Value is the net profit we can obtain from a customer.
• PBP (Payback Period): The payback period for capital investments refers to the time required to recover the investment cost or reach the break-even point. An ideal payback period is about one year.

LTV:CAC Ratio​

The LTV:CAC ratio helps you determine how much you should spend to acquire a customer for sustainable growth.

1. 1:1 = The more you sell, the more you lose.
2. 3:1 or higher = Good.
3. 5:1 or higher = Insufficient marketing investment.

Why Nonviolent Communication?​

To improve communication quality by ==valuing everyone's needs==. ==Judgments and violence are tragic expressions of unmet needs.==

What NVC is not​

• NOT about being nice.
• NOT about making them to do what we want. It's about mutual understanding.

Ways to enhance connection & understanding:​

1. vulnerably express our feelings & needs
   • consciousness of the ongoing feelings & needs
   • vulnerability of exposing feelings & needs
2. emphatically listen to the feelings & needs of the other.
   • Qualities of empathic listening: presence, focus, space, caring, ==verbal reflection of feelings & needs==
   • NOT advising, fixing, consoling, story-telling, sympathizing, analyzing, explaining, …
   • No matter what is said, hear only feelings, needs, observations & requests

e.g. ==Are you feeling … because you need …?==

Ways to alienate us from one another​

• Diagnoses, judgments, labels, analysis, criticism, comparisons, etc.
• Deserve thinking (i.e. that certain behaviors merit punishment or rewards)
  • Demands (denial of other person’s choice; intention to punish those who don’t do it)
  • Denial of choice or responsibility (had to, should, supposed to, they made me do it, etc.)

A Bloom filter is a data structure used to detect whether an element is in a set in a time and space efficient way.

False positive matches are possible, but false negatives are not – in other words, a query returns either "possibly in set" or "definitely not in set". Elements can be added to the set, but not removed (though this can be addressed with a "counting" bloom filter); the more elements that are added to the set, the larger the probability of false positives.

Usecases

• Cassandra uses Bloom filters to determine whether an SSTable has data for a particular row.
• An HBase Bloom Filter is an efficient mechanism to test whether a StoreFile contains a specific row or row-col cell.
• A website's anti-fraud system can use bloom filters to reject banned users effectively.
• The Google Chrome web browser used to use a Bloom filter to identify malicious URLs.

A skip-list is essentially a linked list that allows you to binary search on it. The way it accomplishes this is by adding extra nodes that will enable you to 'skip' sections of the linked-list. Given a random coin toss to create the extra nodes, the skip list should have O(logn) searches, inserts and deletes.

Usecases

• LevelDB MemTable
• Redis SortedSet
• Lucene inverted index

A skip list is essentially a linked list that allows for binary search. It achieves this by adding extra nodes that enable you to "skip" parts of the linked list. Given a random number generator to create these extra nodes, a skip list has O(log n) complexity for search, insert, and delete operations.

Use Cases

• LevelDB MemTable
• Redis Sorted Set
• Lucene Inverted Index

A Bloom filter is a data structure that is used to determine whether an element is a member of a set with a much higher space and time efficiency than other general algorithms.

The results obtained using a Bloom filter may yield false positive matches, but cannot yield false negative matches. In other words, the query returns results that are "either possibly present or definitely not present." Elements can be added to the set, but cannot be removed (although this can be addressed with an additional "counting" Bloom filter); the more elements added to the set, the greater the likelihood of false positives.

Use Cases

• Cassandra uses Bloom filters to determine if an SSTable contains data for a specific row.
• HBase Bloom filters are an effective mechanism for testing whether a StoreFile contains a specific row or row-column cell.
• With Bloom filters, a website's anti-cheat system can effectively deny access to banned users.
• Google's Chrome browser once used Bloom filters to identify malicious links.

• CAC: Customer Acquisition Cost is the cost to convert a customer to buy a product/service.
• LTV: Lifetime Value is the estimated net profit we can make from a customer.
• PBP: Payback Period in capital budgeting refers to the period of time required to recoup the funds expended in an investment, or to reach the break-even point. An ideal PBP is about 1 year.

LTV:CAC Ratio​

LTV:CAC Ratio helps you determine how much you should be spending to acquire a customer, so that you can achieve sustainable growth.

1. 1:1 = lose money the more you sell
2. 3:1 or better = good.
3. 5:1 or higher = under-investing in marketing

==Economic Moat== refers to: A company's ability to maintain a competitive advantage over its rivals, protecting long-term profits and market share.

Elements that do not constitute an economic moat:

• Technology. Technology will ultimately be replicated.
• Extensive reading. ==Reading can only help one keep pace with others.== In the industry, everyone reads a lot of books; even reading more than others does not necessarily make you more competitive.
• Master's degrees or other degrees from top universities. These degrees often lead to high salaries, even if they are in stark contrast to what successful investors do.
• Experience. Some degree of experience is necessary to participate in the economic game, but in certain cases, this experience may not be helpful.

Elements that constitute an economic moat:

1. Economies of scale and scope. For example, companies like Walmart, Home Depot, and Lowe's.
2. Network effects. For example, eBay and Mastercard.
3. Intellectual property, such as patents and trademarks.
4. High customer switching costs. For example, Paychex and Microsoft.

In summary, to choose a tool for the public API, API gateway, or BFF (Backend For Frontend) gateway, I prefer GraphQL for its features like tailing results, batching nested queries, performance tracing, and explicit caching.

==Economic moat==: a business' ability to maintain competitive advantages over its competitors in order to protect its long-term profits and market share

Those who are NOT sources of an economic moat

• technology. technology will always be duplicated
• reading a lot. ==reading only makes people keep up.== Everyone reads a lot in this business. Some read more than others, but it does not necessarily make you more competitive.
• an MBA from a top school or any other degrees or designations. This often gives people a big paycheck even though it is the antithesis of what a great investor does.
• Experience. In order to play the game, some level of experience is necessary, but at some point, it doesn’t help anymore.

Those who are sources of an economic moat

1. economies of scale and scope. e.g. Wal-Mart, Home Depot, Lowe’s.
2. network effect. e.g. eBay, Mastercard.
3. intellectual property rights, e.g. patents, trademarks.
4. high customer switching costs. Paychex and Microsoft.

Jerry Neumann: A taxonomy of moats.