In this paper we show how to use drift analysis in the case of two random variables X1, X2, when the drift is approximatively given by A • (X1, X2) T for a matrix A. The non-trivial case is that X1 and X2 impede each other's progress, and we give a full characterization of this case. As application, we develop and analyze a minimal example TwoLin of a dynamic environment that can be hard. The environment consists of two linear function f1 and f2 with positive weights 1 and n, and in each generation selection is based on one of them at random. They only differ in the set of positions that have weight 1 and n. We show that the (1 + 1)-EA with mutation rate χ/n is efficient for small χ on TwoLin, but does not find the shared optimum in polynomial time for large χ.