Why isn't striving for betterment considered opposition to Allah's will?

For example, if a parent has a disabled child, they shouldn't try to give medical treatment to their child to make them "normal." Allah says in the Quran that He will test you with hunger and loss of property and lives ([2:155](https://quran.com/2/155?translations=20)) . Taking this verse into consideration, no one should make an effort to overcome obstacles and hurdles that have been sent by Allah. Striving for change means you are "challenging" the will of God indirectly. So why is it not considered disbelief? The only thing you should do is practice sabr (patience) and accept it as it is.