How to fix unsmooth linear rails?

There are many reasons to make linear carriages move unsmoothly. Collisions during transportation are one of the main reasons. Here has an easy way to fix the issue, gently hit each position of the carriage. Why does it work? The unsmooth is caused by the dust caps on the carriage stuck on the rail. Hitting could move the caps slightly away, then the carriages run nicely again.