Sometimes this perplexes all sellers. The main two reasons a home sells are 1. Price & 2. Condition... a very close third in my opinion is marketing. How many showings are you getting? If you are getting a lot of showings, but no offers; then price may be a bit too high. Also, feedback from each buyer should be requested by your listing agent.. sometimes listening to feedback holds a world of difference from getting it sold to expiring. As the last two agents mentioned, timing and competition are also large factors that can influence supply vs. demand and thus give you much more time on market. I would add that you need to get a timing analysis done on your market area so you can feel more comfortable knowing what's going on. If average days on market is 130 and you have only been on the market for 60, then you shouldn't be panicking... however if you are way over average days on market AND adjusted days on market.. then it may be time to sit down w/ your Realtor for a little "come to Jesus" time!
Hope that helps and best of luck selling