Establishing yourself as a scientist takes an awfully long time. The riskiest part is learning what a true scientist is and then taking the first shaky steps down that path, which will become a road, which will become a highway, which will maybe someday lead you home. A true scientist doesn’t perform prescribed experiments; she develops her own and thus generates wholly new knowledge. This transition between doing what you’re told and telling yourself what to do generally occurs midway through a dissertation. In many ways, it is the most difficult and terrifying thing that a student can do, and being unable or unwilling to do it is much of what weeds people out of Ph.D. programs.
The optimist sees the glass half full. The pessimist sees the glass half empty. The chemist sees the glass completely full, half in liquid state and half gaseous, both of which are probably poisonous.