I got to thinking the other day about some common mistakes hunters make that cost them.  Now lets assume that a "successful hunt" means taking an animal.  I know that is not always the measure of a successful hunt but lets say it is for this discussion.

1. Equipment and Practice
    When you do everything else right (or get really lucky) and there is your animal standing broad side in front of you, failure should not be because your gun will not work, is not sighted in, you forgot to bring the right ammo, your scope is fogged up, you can't get the gun on your shoulder because of your big down filled coat...

All these things you have control over and should have got figured out long before you entered the hunting woods.

2. You are not ready to make the shot.

Often the chance you get at an animal only lasts a few seconds.  If you need to load your gun, take off the scope covers, take off your sun-glasses or generally "diddle around" you are likely to miss out on some opportunities.  You hear a lot of stories like "I saw this great buck but I could not get a shot because..."  Often the because was they were not READY to act quickly.

My father-in-law went to a spot I had lined up for him.  Later he told me he had seen the biggest buck he had ever seen but could not get a shot.  The buck stepped out and his gun was leaning up against a tree a few feet away.

3. Two or more hunters are out together and have not made a plan for what to do if they encounter an animal while they are together.

If you want to let the other guy have the first or best chance at a deer you had better get this sorted out with him before you are standing looking at a buck that is ready to bolt.

What other "screw-ups" or lack of preperation have you done or seen that cost getting the game.

Being in proper shape for the hunt and spotting.  If you're tired, your head is down when you're walking, don't care who you are.  You're also noisy.  If you find yourself walking with your head down, sit for awhile.  Enjoy what's going on around you.

If your hunt involves spotting with bino's or a spotting scope, Do it, regularly!  I once got a nice buck because I saw his breath from almost a mile away.

If hunting in more dense brush, for goodness sake don't be in a hurry.  The only animal that walks nonstop is a human.  Listen, look.  If you don't you'll walk past more animals than you'll see, and odds are they buggered off 5 minutes ago 'cause they heard you walking with your head down.

Most important, patience, and don't get frustrated.  If you put in your time you WILL get your chance.

Lastly know what you're comfortable with and stay in that comfort zone.  Son got a nice buck a few years ago.  We hunted that same buck for four days.  He had two previous chances at it.  The first was about a 60 yd shot walking;  son didn't shoot.  I asked why?  Son, "I was shaking too bad and didn't want to take the shot".  On day 3, again from about 60 yds, walking. Son, "the angle just wasn't right".  The kill shot was from just over 100 yds, broadside, bang flop.  I was happy he got his big buck, I was proud that he knew when to pass.

I have only hunted one thing in my life besides my very first deer and that’s Big Horn sheep. 

The rest has mostly been for pure enjoyment I would rather shoot one grouse off a good point from my dog then swat my limit off the road.
 
  I have seen some epic F ups one real good one that involved a scope cranked to max power when we knew there was a good 170 ish Muley bedded down in some tall grass walked over to flush it out and pard couldn’t find it in scope.  What wrecked his day was my benefit we got to keep hunting.
 
 As I get older I find more enjoyment watching others.  I have wanted to catch a marlin for most of my life last year I had the opportunity rented the boat guide the whole deal set out for the day.  My plan was to catch a 700 pounder even the guide would have got to fight it as he yelled at me driven the boat.  When that reel started to scream wife was first one up we had no idea how big it was didn’t see it for the first 20 min.  With the wife still fighting it the marlin leaped out of the water a good 300m back I asked the guide what he thought it would go his reply was 300 pounds at least, it’s a good one.  2 hours later with the wife about to give up we had it at the back of the boat took pics and I cut the line.  Not for one second do I wish I was the one that caught that fish.             

Being impatient, rattling in a good spot and not waiting long enough, then moving and spooking a big deer.

Over thinking things.

Moving to fast to a "good spot" only to spook animals.

BruceW brought up a lot of tips I go by. The one thing not mentioned at least i don't think it was is the follow up after the shot. Even if you don't think you hit your animal always check for blood or hair. I've found a big deer or 2 one I know for sure was shot by a hunter and he said" it didn't look like he hit the animal". 3 years later I found  beautiful 5x5 that measure 1" under book after sitting in a cutblock .I have no respect as a hunter for these idiots, even if they stumble upon their animal a few days later because the ravens are all over it and attach a tag.