What's your basis for asking hikes?

"I need a 30% hike, " said 2 of my colleagues who belonged to two different teams. They had contrasting performances.

One was at 100% sales achievement and the other at about 60%. Interestingly they both had one commonality, they were the topmost performers in their team :)

The demand for their hike was stimulated by an external source. It seems both had recently received job offers from different employers with a 30% raise. The 100% achiever knew the dependency her supervisor had on her and maybe wanted a payback for her performance.

The 60% person had nothing to lose as his benchmark was his prospective employer's offer. I met both of them to understand their context. The first one implied that every year its difficult to achieve 100% and hence it's important to feel recognized. The second person gave me an impression that "you can't have a bad increment for one average performance and life needs to go forward with the immediate opportunities."

I am sure every year we get higher offers from other innocent, desperate employers who decide our value based on the 30 minutes interview time. And we decide their value based on the 30% they offer us. Mutually convenient? What's your basis for asking hikes? Peers, EMIs, Marriage, Kids?