Side effects in life
There’s a side-effect to absolutely everything you and I do. Exercise, for example, allows you to not only grow stronger and fitter but also gain knowledge about your body. You’ll learn your limits; both physical endurance and mental resilience.
If you practice meditation, you’ll know that it takes a bit of time to empty your mind. During that period of transition chances are other thoughts creep in to fill the void. For me, this is both annoying and beneficial. Annoying because it’s hindering my true purpose: a clear mind. Beneficial because it gives these thoughts free reign, effectively freeing them from whatever activity you were occupied with before your failed (or successful) attempt at meditation. Lateral thinking is usually accidental.
There’s a bunch of ancillary benefits to exercise I’m learning about as I grow fitter/happier/more productive. You learn about your body’s limitations, and how to push them.