DeusMalum

He sacrifices for the greater good.

Now what is the sacred timeline? In the sacred timeline, whatever you do, the future won't change. Like in the previous example, what if the meeting of his parents happened because of him? Then it will be necessary for him to come to the past to let his parents meet. And the best part is that he will never know that when he visited in the past, he was used as a catalyst, not a variable.

It can. Imagine a 20-year-old boy invents a time machine and goes back 21 years to see how his parents met. After coming to the past, he runs to the place where his parents met. While running, he collides with an ice cream seller, but he keeps running to the spot. Now, when he reaches the place on time, his parents do not meet. He disintegrates. Now in this timeline, there is no future where he is born.

There are many variations, and the variations are the prime cause for having so much timeline. That's why even TVA has strict rules and regulations to cause the least variation in history. Even one mistake in the past can erase the whole future.

* will doom.

Correct me if I am wrong, but no one can see the future. Even the ancient one. He/She can deduce probabilities. There are always variations they haven't even imagined. If someone gets reincarnated in the MCU, he will be just a variation. He/She just has to take the result of your appearance and again deduce possible futures. Even Dr. Strange (the possibly strongest and wisest magician) only sees future possibilities. If they start eliminating variations, the whole world will doom.

If he/she let it happen, it is for a reason. We humans sometimes question him/her for our own fault and blame him. Humans sometimes also forget that God is not exclusive to humans only; the universe is too big and we are not even the size of dust in it.

Best Advice!

What's bad in it? If I have no food for more than 4-5 days, I am eating it. Oh, sorry, I will feast on it.

Your sentence here has many interpretations.