How can one differentiate between being content with divine decree (Qada' and Qadar) and striving to change and improve reality?

A Muslim must be content with Allah's decree, thankful for blessings, and patient in adversity. He should strive for what benefits him and exert effort to achieve his goals, seeking Allah's help, and not despair. For the strong believer is better and more beloved to Allah than the weak believer. And if something befalls him, he should say, "Allah has decreed, and He has done what He willed." Striving for benefit and seeking good does not contradict being content with Allah's decree.