I think overcoming our own biases. For example it often happens that random streak of profitable trades coming after you started to apply some "system" inevitably makes you think that you found right method for trading. If it fails later you start to think that it needs to be fixed not that it doesn't work at all because it's hard to challenge assumption that it works (as it came from your positive experience). This is how our brain works. Many years people with this bias just trying some useless stuff.
If any difficulties arise, stop and remember what needs to be done in order to be able to solve them easily and quickly
The most important thing is to learn how to overcome all problems and make a positive moment out of it.
The biggest hurdle for a small investor is time, he has to manage time for his work, family, personal and then trading also, which requires quite a lot of time.
The biggest challenge is finding right trading approach which is based on sound logic rules, avoids using technical analysis BS and also have strict risk control parameters.
All problems can always be solved and drawn from them, and a conclusion that will eventually be useful to you in the future.