Here's something that you don't see discussed very often, but it's worth some thought: what kind of personality do you need to have to do drug discovery research? Clearly, any conclusions are going to carry over well to other fields, but drug work has some peculiarities that can't be ignored.
The most obvious one is that the huge, horrible, overwhelming majority of projects never lead to a marketed drug. Many readers will have seen the sobering statistics of 85 to 95% failure rates in the clinic, but (bad as that is) it doesn't get across the number of times that projects get nowhere near the clinic at all. Take it from the top: the majority of targets that are screened for chemical matter don't turn up anything useful (it's not even close). The majority of the ones that do still die on their way to clinical trials. And then a solid 90% of those don't make it to market.
So, if you define yourself as a success by whether or not you've put something on a pharmacy shelf, you've set a very high bar, one that many people in basic research don't reach. It's different for people further down the line, where the field has already narrowed. But if you're working on early med-chem, for example, you're likely to go years between realistic shots at a drug you can claim part of the credit for.
That'll vary by your company's culture, too. Some companies bang out projects like a sawmill spitting out boards - or try to, anyway - while others carefully take their time for years and years. There's no certain advantage to either method, as far as I can see (else the companies doing the best one would have taken over by now and driven other modes out of existence). But you'll certainly have more shots on goal at the first type of company, which might keep your spirits up. Of course, the fact that you're largely going to be getting more chances to fail in the clinic might just depress them again, so you have to take that into account.
It'll also vary by therapeutic area. Central nervous system projects are going to run slower than oncology ones, by and large. In cancer, the clinical goals are comparatively clear, and where the disease is often (and most terribly) progressing at such a pace to give you solid numbers in a reasonably short period. Contrast that to Alzheimer's disease, for example, whose ruinous clinical trials could take years to tell you anything useful. Cancer will also give you more shots per compound, since a drug that does zilch for pancreatic cancer (and most do just that) might be useful in the lung or liver. While what we call cancer is several hundred diseases, what we call Alzheimer's might only be one. Depression and schizophrenia are clearly more complicated and split up, but (as opposed to cancer), there's no easy way to tell how many types there are or what particular one a patient might be presenting with, so the clinical work is correspondingly more difficult.
So, this is the pharmaceutical world you're going to have to live in. If you take each drug project personally, as an indicator of your own worth, you're probably not going to make it. You'll be beaten down by the numbers. As an antidote, a bit of realistic fatalism is helpful, although too much of it will shade into ah-that'll-never-work cynicism, which is the ditch on the other side of the road from prideful optimism. I'd recommend learning to enjoy the upside surprises, and to not be surprised by the failures (while still looking them over to see if there's something you can avoid next time around). You really have to draw a line between the things you can affect through your own talent and hard work, and the things you can't. Most of the crucial stuff is in the second category. A sense of humor about your own abilities and limitations will serve you well. But that goes for a lot of other jobs besides the drug business, doesn't it?