This made a lot of sense , so here goes ...... simply put ....
Everything is predetermined. Who determines this , we dont know. If things were not predetermined , there would be chaos in the Universe. The moon & the Sun would rise at their own will, the Ganga would flow from Calcutta towards the Himalayas.
Karma , is also part of destiny , as are self-will, sel-effort, even ego & patience. Everything comes as a part of our destiny, but within the rules !
The thought that I am free & I can do anything is not true. Everyone & everything is bound by some rules. Ritam cha Satyam cha, say the Upanishads. The universe depends on the 2 rules of Ritam & Satyam. RITA means Natural law. SATYA means the Reality. An incident happens; Satya is what happened & Rita is the rule according to which it has happened.