I have come accross Salkind's analogy pertaining to these things,
You can have the sexiest-looking car on the road, but if the tires are out of balance, you can forget good handling and a comfortable ride. The tires, or where "rubber meets the road," are crucial. In the same way, you can have the most imaginative research question with a well-defined, clearly articulated hypothesis, but if the tools you use to measure the behavior you want to study are faulty, you can forget your plan for success (Salkind, 2006).
To understand the above statement in a very simple way, I list few equations below:
Validity = Any concept that we state = Any concept that we intend to measure
Reliability = We conduct the same measurement for thousand times = We still get the same value
(remember, reliability only explains about scores, not about individual, subject or respondent)