You certainly can do a "For Sale By Owner" yourself. Lots of people do. On the other hand, most of the people who start off FSBO end up using a Realtor. But it's certainly possible to do it yourself. If you want, give it a try.
Can you do it easily? No. As Mack says, it often isn't easy even for professionals. There's a huge amount of work that you don't see, all of which has to be done properly. Plus lots of marketing. Often, lots of negotiation. Honestly: If it were easy, everyone would do it and there'd be no need for Realtors. So: Easily--no. Possible--yes.
Is it worth it to use a Realtor? Almost always. When would it not be worth it? A private sale, maybe between family members, when the questions of value, the need for negotiation, and so on aren't significant. In that case, it'd make more sense just to go to a lawyer. Or for a period of a year or two back in 2005-2006 when any property seemed to sell almost instantly . . . when getting financing wasn't a problem . . . when there was no problem pricing a property above what your neighbor's sold for last week because someone was willing to pay more, the appraisers were willing to give a high appraisal, and the banks were begging borrowers to take their money.
But now, when it's gotten a lot more difficult to sell, when your marketing needs to be effective, when your home has to show well, when lenders and appraisers have tightened up on their criteria--yes, it's almost always worth it to use a Realtor.
Hope that helps.