Stability in both direction, we have to avoid levels where there are large drops for the next level.
You never really fix anything in trading, if you see a peak it means that value might be over-optimized, it might mean you had some lucky picks in the history which will never come back, if on the contrary you have similar results around your choice it means that actually that area is really leading to good results.
Imagine a strategy buying between 10 am and 11 am and then selling at 1 pm (just an invented example), you try to figure out what time it is best to start if at 10 or 10:30 so you run an optimization step 5 minutes. now imagine you have many good trades starting randomly between 10 and 10:15 but one single case at 10:20 when you got a huge profit due to some news, well, your optimization will show that 10:20 is the best time to start showing maybe a drop at 10:25 (imagine all the move took place in those 5 minutes), while at 10:15 you make less money, so your idea would lead you to choose 10:20 ignoring it is due to a pure coincidence and that actually from 10 am on there is a tendency to move in that direction.