To expand on 1, I think it's been important for me to have some anchor points along the way. Some things I can "accomplish" however small they may be that, if nothing else, help me feel like I'm making progress I won't lose, even if full understanding takes much longer. Otherwise, backsliding in interest can mean the next time I get interested, I'm faced with the prospect of starting over from scratch, which can sometimes mean I just move on to something else.