Psychological research has proven it takes 10,000 hours to be an expert in a given skill.
Just over 416 days.
If you studied day and night!
Broken down to 8-hour days, it would be 3.4 years.
Considering that would be the equivalent of a full-time job (and some) you are talking more like four or five years to achieve the mantle of an expert within your ''skill''.
However, there is a variant in the level of expertise. Consider an expert chess player. You may have someone who is a smart club player to a Grandmaster chess player. The likes of Bobby Fischer (1943 - 2008). These rare talents could be concluded as exceptions to the rule. On a statistical criterion, they would be in the top 1%, and more likely a fraction of a percent. There are 800 million chess players in the world and only 1500 Grandmasters. So the percentage chance of being a Grandmaster chessplayer is 0.0001875%. That is probably the chance of Joe Bloggs beating such a player.
Clearly, chess is a complex game. To be a quality player (better than most) takes skill and innate biological capacity. Like so many talents, it goes beyond time spent learning. But consider this to gambling. To achieve a skill of lofty expectation you need to find a niche and hone your skills. There are many types of poker players, although all playing the same game, same cards, and percentages. But the variety of skills, to beat your opponent(s) can be many and varied. In this day and age, players view their skills including chance on a statistical level and psychology to understand tells (to know a bluff when they see one or try to hide their bluff like a master chess player).
Horse racing is a very open-ended subject/niche from a gambling point of view. It has an improbable number of variables. But, as seen with the psychology hypothesis, you need to limit the number of variables to improve your chances of winning. That's why it is important to find a niche. Each to their own, but the approach of thinking you can bet on anything and everything horse racing is a ridiculous idea. Why? Simply because there isn't enough time to do all these things. To master a broad subject matter compared with something specific like your chosen subject on Mastermind. In truth, you don't need to know everything from a global perspective. If you know your niche subject well you simply need to double your stake rather than double your skillset. It makes sense. It is the equivalent of doubling your brainpower.
When you consider it takes 5-years to be an expert within your chosen niche within horse racing betting, (in truth, it will take much longer) you don't have time to waste. Also, this expertise is hard-fought. You need to have a plan, idea, assumption (at least) which takes you on a journey that separates you from the crowd. You cannot afford to follow the crowd, because statistically and logically, it would seem very unlikely you can defy the odds.
Your understanding should be carefully assessed. You may wish to follow a blind approach but it is a wise decision to have an understanding of your progress.
To be a successful gambler is similar to being a top-class chess player. It reveals itself in the confidence you have in beating your opponent or layer. You are pretty certain, if not almost guaranteed, you will win long term.
If you don't look at your opposing number and feel you can win you really need to hone your skills or, at least, take on an opponent you are confident you can beat.
Good luck on your journey.