Don Quixote titled at windmills, in other words treated as powerful enemies powerless objects.
To tilt at windmills is thus to treat trifling annoyances as major problems.
It is easy to see minor irritations like someone's cross word, a lost letter, or a broken cupboard door as trifling annoyances.
The trick is to apply the same logic to other things, which appear large, and which 'common sense' would tell us are important.
The 'size' of these affairs is not their size in the world's sense but their importance to me.
My 'life' is actually a trifling matter. The apparent threats to it, in the light of the power of God: also trifling.
The only thing that is not trifling is the question of devoting my life to doing God's will.
That is the only matter worth my attention and concern.