What is the difference between qadar (divine decree) and luck? This is, if there is such a thing as luck.

A person experiences neither good nor evil except by the decree and will of Allah. Belief in divine decree, both good and evil, is a fundamental pillar of faith. What people refer to as luck is a success granted to some individuals by Allah's decree. The "lucky" person does not obtain what has not been decreed for them. This belief is invalid according to scripture, reason, and reality. The Prophet, peace and blessings be upon him, said: "O Allah, there is none to withhold what You give, and none to give what You withhold, and no fortune benefits a person of fortune against You."