you must (learn to) walk before you (can) run
One must understand or become adept at the basic skills, techniques, or details of something before moving on to that which requires greater skill or experience. I see it all the time: people who want to become hotshot doctors but don't want to put in all the hard work the field demands. You must walk before you run. While the results of the drug trial are encouraging, there are still a huge number of tests we must run—after all, you must learn to walk before you can run.