is there any way by which we can predict the growth/loss of a mortgaged backed securities or any other assets

as you mentioned, that 2008 crisis - lehman brothers bought mortgaged backed securities and predicted/assumed that they will grow in the future but it didn't happen.
so, what was the assumption of growth based on? how did they assumed that it will grow? any particular reason?
when we take such assets, what decisions should we take into account while choosing whether to buy or not? (if there are any points to discuss)