The attempt to combine two liquids that do not normally mix with the aid of an "emulsifier" is known as an emulsion. Because hollandaise classifies in this category, it may take a few tries to get it right. Quite commonly, a hollandaise may "break," which means the two liquids separate, and your sauce becomes watery and alas, incorrect. To avoid this, the hollandaise must never get too hot, too cold, or have too much fat added at one time. To be safe, make your hollandaise right before you are about to serve it.
Don't get discouraged; practice makes perfect...and perfect eggs benedict!