Unless you invest in start-up companies without rearview results, you are always using the rearview to forecast the frontview to some extent. For most companies that interest me, the immediate road behind looks like a great, smooth ride. However, the frontview is foggy with a winding and bumpy road.
Companies with long driving records can inform you how they have dealt with past roads and how they will deal with difficulties in the future.
To take the metaphor one step further, I like companies where the road behind is of the same kind as the road ahead–no amphibious vehicles required. Blackberry changing from a handset maker to a software company is like trying to drive a BMW over the ocean. It may have been a great ride through the countryside, but I am not sure how it is going to handle on the Atlantic.
The rearview mirror can tell you a lot about the frontview as long as you are still on dry ground.