If Bob is renting, then when the situation changes he risk losing a house over his head. That could be: 1. if the landlords decide no longer to rent the property (e.g. if they retire or move abroad); 2. if he is priced out of the current area due to increased rent; 3. if he retires and no longer has the monthly income to sustain paying rent; 4. if he gets a girlfriend or boyfriend and they want a bigger place, or if he has a child; 5. if he wants to modify the house in some way (e.g. change a room into a child's bedroom, or redo the kitchen/laundry area to add a new device, or replace the shower or boiler with a more eco/environmentally friendly one).

Or are you saying that he should become homeless?

> If Bob is renting, then when the situation changes he risk losing a house over his head

I hope you don't want to claim here that buying a house means that you cannot ever "lose a house over your head"? Because that would be plain wrong. And if you just wanted to say that it reduces the chance, then you should have some good arguments.

Also, some of your points are strange:

> 4. if he gets a girlfriend or boyfriend and they want a bigger place

Well then it's much easier to move to a different place, rather than buying a new house and selling the current one, don't you agree?