Forgive the excessive length. I only post here once in a blue moon these days so there's a lot of thoughts to get out when the mood strikes.
If I were to give someone advice who is just starting out studying the market, regardless of the instrument or type of security, it would be to begin studying and developing an understanding of underlying market behavior and movement, however, that's just me.
There are a variety of ways to succeed in this industry. I'm sure there are some individuals who grind out a large volume of razor thin +EV trades using statistics, or are capitalizing on intelligently captured premium, or boost their returns with superior hedging techniques, etc.
I've seemed to come across four types of mindsets about the market in environments like this. Sometimes they overlap slightly;
1. Participants using a bland yet tried and true strategy; like buy and hold with a diversified portfolio. The market interests them and they like to talk about it or study, but they don't do anything more complicated than that for a myriad of reasons.
2. Participants who develop an intelligent understanding of the conventional market practices like above, and seek to optimize them to enhance their returns. Seems like you've done or started to do this with value investing vs. just holding an index, for example. Other low-hanging fruit to enhance returns without much complexity or advanced study is the strategic use of very slight leverage to increase returns over time while still keeping a near 0% risk of ruin using basic past market statistics, or basic hedging techniques using long-term options in certain ways to slightly elevate the r:r over time of a portfolio.
3. Traders and individuals that design and also have the mental capacity to execute much more precise systems that tightly control risk and exploit environments that provide very favorable returns to those controlled risks. The more precision a system has, and the more consistency a user of such is able to operate with, higher leverage can be used as well to greatly enhance returns.
3b. A mass of individuals who think this is possible, and are either slowly building the skills needed to operate this way, or far more likely are just spinning their wheels trying to attain something they don't have one or many of the tools required to do so (mental organization, emotional control, free from delusions, etc.)
4. Cynics at varying levels of pessimism. Either due to their personal experiences or set of beliefs about the market, they usually heavily doubt, flat-out disbelieve, and are even hostile toward the idea of #3, even though there is plenty of evidence lying around that a small group of people are able to do things like this consistently. May even doubt any optimization over the broad-based market is possible or something [which is absurd to me].
You've got to decide which bucket you want to put yourself into before you go any further. How much of your time and vitality are you willing to pour into the market. Are you going to be able to stay optimistic and motivated despite set-backs? Can you approach this in an intellectual manner or are you going to be driven by your emotions? Are you patient enough to properly equip yourself with everything you need to interact successfully with the market at a given level before you attempt to do so?
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Anyway, to try to get back to the topic at hand, I think you've started in the right place. Investigating whether something is possible before commiting yourself to it. The answer to your question is yes, 20% per year can easily be achieved over a long period of time, and even blown out of the water significantly.
If you need convincing of that fact, just think back to your experiences at poker. You should have a massive amount of experience with the fact that humans fail very often at being rational. A man, even who knows how to play poker quite well, might play a sub-par hand in a poor position simply because he lost control of his emotions.
Others might content themselves with learning just enough about the game to be entertained and bleed slow losses over time, but they don't care. Good players with a good game might get impatient for money and take excessive risks because of it. They might even make perfect decisions and still get blown out by playing far above responsible stakes for their bankroll.
The market is no different. People don't always buy and sell where reason dictates. The greater amount of emotion there is in the market; the greater opportunity there is for those who can capitalize on it. There are some killer strategies that can be designed that will take a position a couple times a month with huge r:r based off certain context. Sometimes there are price insensitive positions being taken or closed by large entities that also represent great opportunities for smaller participants to quickly disseminate.
Even in present day, the market is a huge source of opportunity for individuals who are capable of utilizing it. You're going to hear a lot of conflicting opinions, pessimism, discouragement, bits of wisdom, vague platitudes, and more around these environments. No one can decide for you whether 20% returns per year are possible or not. If you continue to directly study and learn for yourself with an open mind I think the answer becomes clear quite quickly. But that's just my own belief; your mileage may vary.