In life you must often choose between getting a job done or getting credit for it. In science, the most important thing is not the ideas you have but the decision which ones you choose to pursue. If you have an idea and are not doing anything with it, why spoil someone else's fun by publishing it?
As quoted in "Some Szilardisms on War, Fame, Peace", LIFE magazine, Vol. 51, no. 9 (1 September 1961), p. 79