Luck.

300 bookmarks/60 summons is not that much, unfortunate as it may be.

Try your best and play with the hand you're dealt, that's the only way.

Unless you are willing to spend more money than a car on this game.

If you think every banner only need 200 bm to pull, then there would be no pity in the first place. 

Why would they implemented guaranteed after 120 pulls / 600 bm if people only need 200 bm to get the hero?

Logic.

You got lucky, that is all there is too it getting the unit in 200 BMs. I have two accounts. Sometimes one account will hit pity twice in a row while the other will get the unit in 200-300 BMs.

Its clearly listed as a 1% chance for the pity banner so you really shouldn't expect to get it after only 40 summons aka 200BMs. Everytime you decide to summon on a banner you should ask yourself this "Do I really need this unit? Do I really want this unit? Am I ready to go to pity for this unit?" If the answer is "No" for any of those then don't summon.

So, You are complaining about last limited SS. Belona banner around 2 months ago now?