You can easily overlook details you meticulously labored over in the past and fail to appreciate how much of it is now way over your head. You cannot assume you're "better" today just because you have more experience.
In fact, experience does have a tendency to throw away critical insights and give an arrogant and false sense of confidence. This doesn't only apply to judging your own work either. Just because something "worked out" for you doesn't mean you were right. Just because someone less experienced than you tries a different approach doesn't mean it can't work or maybe even be better than what you think you know now.
How many people spend too much of their later lives settling for the same patterns over and over wondering where their creative edge went? There it is, and it's all because you thought you figured something out that you never really did.