One good way to ensure that your plans are robust is to strawman yourself. Look at your plan in the most critical, contemptuous light possible and come up with the obvious uncharitable insulting argument for why you will fail.
In many cases, the obvious uncharitable insulting argument will still be fundamentally correct.
If it is, your plan probably needs work. This technique seems to work not because it taps into some secret vault of wisdom (after all, making fun of things is easy), but because it is an elegant way to shift yourself into a critical mindset.
For instance, I recently came up with a complex plan to achieve one of my goals. Then I strawmanned myself; the strawman version of why this plan would fail was simply "large and complicated plans don't work." I thought about that for a moment, concluded "yep, large and complicated plans don't work," and came up with a simple, elegant plan to achieve the same ends.
You may ask "why didn't you just come up with a simple, elegant plan in the first place?" The answer is that elegance is hard. It's easier to add on special case after special case, not realizing how much complexity debt you've added. Strawmanning yourself is one way to safeguard against this risk, as well as many others.