You can, but you should install more than one module of the same size to ensure optimum performance.
As far as memory goes, computers are built to work with modules of any capacity so even upgrading RAM will run into this problem. To get around this problem, users can opt for multiples (install twice as many modules) or choose different sizes (install 2×4 gigabytes instead of 1×8; 2×8 instead of 1×16). Memory is best installed in matched pairs to maximize compatibility and performance. Please visit your computer manufacturer’s website for instructions on memory installation.