As-Salaam alaikum,
The thought may occur in some minds that what would they need Du'a (Supplication) for, when everything is Destined to happen the way Allah, Azzah Wa Jallah, has ordained!!

No, that is a wrong perception... Du'a/Prayer/Suplication includes averting affliction... it is a means of turning aside tribulation and drawing the Divine Mercy, just as a shield is a means of deflecting arrows; and water is a means of bringing forth herbage from the earth.

Just as a shield turns aside arrows and they offset each other, so too supplication (Du'a) and affliction compensate each other. It is not a condition for believing in the Destiny of Allah Most High that one go unarmed, for Allah has said:-

"TAKE DUE PRECAUTION". (4:71) or that one should not water land after seeding, saying:

'If previously destined the crop will grow, and if not previously destined it will not'. Rather, the conjoining of causes and effects is the premordial destiny that was accomplished "in the twinkling of an eye or even faster." (16:77).

So, stick to Du'a always... regularly as the Noble Messenger of Allah, Sallallahu alaihi Wasallam, said: "Du'a is worship".... he also said: "Whoever does not ask Allah, He becomes angry with him."