The product of an aldol reaction is a $\beta$-hydroxy ketone. This can go on to eliminate to form an alkene thus:
However, the species on the far left of the above diagram (the $\beta$-hydroxy ketone product of the first aldol reaction) can react through an aldol reaction again given that it has two more available protons at the $\alpha$ position.
How is it possible to tell which reaction pathway will occur? Is this the issue that is referred to when the Aldol reaction is referred to as "hard to control"?