Why yes, you decide, I should definitely apply to an accelerator. But your buggy imagination failed to mention a few things – like, for example, what happens between getting accepted and demo day. It forgot to imagine how it would feel to be on the bottom of your accelerator cohort, or to argue with mentors, or to have a barely-working prototype for demo day. I’m not saying this will happen to you, but it might. Accelerators add enormous value to startups, on the whole. But some accelerators don’t, some mentors don’t, and some entrepreneurs just don’t put in enough work to capture that value. If you’re thinking about joining an accelerator, be prepared for these harsh realities:

Mentors aren’t omniscient

“YC and Paul Graham don’t have all the answers. They can point you in the right direction and away from the wrong paths, but ultimately the founders need to make it happen.” – Lee Lin, founder of RentHop (Y Combinator) “Mentors will come in and claim to have an understanding of your business, but the reality is: no one knows more about your business than yourself.” – Ted Hadjisavas, CPO at Everlab “Lawyers circled the group like vultures until everyone was incorporated and then they disappeared. Some advisors, including the preferred lawyers, gave very, very bad advice – in one case, flat-out inaccurate advice (regarding the corporate formation, what an S-corp is, etc.).” – Kate McKeon, CEO of Prepwise Games (Founder Institute) “Entrepreneurs start to believe that the accelerator and their staff has the magic bullet of success. The truth is, all concepts/businesses are different. No one person knows all the answers, so it would be a mistake to believe that they will help solve your problems.” – Chris Sonjeow of LoveBookOnline.com

Programs can be disorganized

“Mentors and investors you expect to be at a meeting did not show. The program staff were constantly scrambling to fill speaker spots to make up for the professionals who did not show.” – Kate McKeon, CEO of Prepwise Games (Founder Institute)

Competition and politics abound

“The odds of a successful company coming out of an accelerator are 1 in 10. By success, I mean million-dollar business. Also, there’s a fair amount of competition between teams to see who will succeed.” – Ted Hadjisavas, CPO at Everlab “After graduation, one bad apple ruined our group camaraderie. We don’t all meet up as a class and talk anymore because it got too competitive between people. Some of us are still in touch, but we would’ve all benefited from a feeling of class unity and continued class meetups. It kinda soured the end of the experience. And it’s sad that it only took one person/company to do that.”  – Reva Minkoff, founder of DigitalGroundUp (Founder Institute)

The schedule is rough

“The program schedule was intense; we basically had no evenings. It wasn’t unusual to have a session until 9:30 pm, and another one at 10 am the next morning. Sometimes I’d pitch our product four times in a single day. In many cases, the sessions required advanced preparation if you wanted to make the most of them, and managing this while my company was gaining traction was crazy.” – Dorin Rosenshine, founder of Outleads (JFE Accelerator) “You’re in the program for 9-12 hours per day for 3 months straight, which can be tough for some people.” – Justin Zhu and Andrew Boni, cofounders of Iterable (AngelPad) “It’s a tremendous amount of work. Accelerators are fairly appropriately named. They are a forcing function that puts the pedal to the metal and that adds a lot of work and stress to the already over-worked and stressful startup day-to-day. It works in the end, though.” – Jonathan Wasserstrum, cofounder of TheSquareFoot (ERA)

Your initial idea might fail

“The worst part of the experience was finding out our entire business model failed. Thankfully, we found out a lot sooner when Paul [Graham] told us to fly back to NY and become real estate brokers for a month! (An interesting story in and of itself…)” – Lee Lin, founder of RentHop (Y Combinator)

Your fate is in your hands

“You get exactly what you put in. We quit our day jobs at Google and Twitter and gave it 110%, so that when we finished the program we had a product that was pretty much ready for the public.” – Justin Zhu and Andrew Boni, cofounders of Iterable (AngelPad)

The feedback is blunt

“A good accelerator does an excellent job of creating stress as a way to force issues to the surface as fast as possible. They do so by exposing every flaw in your product, business plan, and team. This is both the worst and best part of the accelerator experience. Dealing with these challenges is painful, but at the same time doing so successfully is definitely a validating experience.” – Austin Marron, cofounder of Common Form (Techstars)