Hi Carly,
The part of my job as a scientist that I enjoy the least is writing proposals. The money to pay my salary comes from federal research grants from government agencies like NASA or the National Science Foundation. It takes a lot of work to write a research grant proposal and the chances that your proposal will be selected for funding vary from year to year, depending upon the number of proposals submitted by other scientists and the amount of money the federal government has set aside for the program to which you are submitting your proposal. It can be incredibly frustrating to put months of effort into a proposal and then receive a notice that it has been rejected. Waiting to hear if a proposal has been selected for funding can be really stressful too, since scientists can find themselves in situations where they will basically lose their job if a proposal is rejected. Fortunately, there are several opportunities in every field to submit proposals every year, and you can collaborate on proposals with other scientists. Most research grants run for about 3 years, and scientists generally end up working on a couple of projects with different start and end dates, so it usually isn't too much of a problem if one proposal gets rejected. You can always try again in 6 months to a year, depending on where you submit your proposals.
Kris