Developing is done in a sequence of steps and tuning the performance of the development is one of the last steps... An ABAP can do it's trick in many ways. Getting an ABAP to do what it was specified to do is one, but getting it to do it's trick fast is another. Tuning the performance comes down to the developer applying a set of "quality assurance" rules which should always be done.
Whenever performance problems arise, it's a good idea to get the general overview of your selection. In every selection that involves more than one table (thus "in every selection"), the first table to select from is the "base" of your selection. Since everything in SAP can be done in 6 ways (and the excellent programmer could find 4 ...) you can usually change the base or one of the other selections of your processing. There could be a lot of performance improvement to win there. Get into your helicopter and get your overview !