It can be difficult to run a good game. Dungeon Mastering is a performance, and can be very stressful. You have a number of people depending on you to entertain them. That doesn't mean all the responsibiliy lies on the DM to ensure the players enjoy themselves, but only that the players depend on the DM. A player won't enjoy an RPG session if they don't put in some effort, yet none of the players will be able to have a good time if the DM doesn't perform well. The DM could be termed the fulcrum of a session, if you will. Everything hinges on him/her. Thus, being a DM comes with a lot of responsibility, and not everyone is willing to take on the job. Every DM has their ups and downs; nobody is perfect and sometimes we screw up.
My game a few weeks ago is a perfect example of this. The party was traveling to a village where they had learned an evil cult was going to receive a shipment of weapons. On the journey I rolled several random encounters and they stopped at a few towns along the way until they reached their destination. It was at this point that I realized I had neglected to have an event occur at a specific location on the journey. I was so focused on making the travel itself interesting and actually feel like there was some distance between towns that I had forgotten about the adventure. I faced a dilemma, either I could improvise and move on in the adventure as if nothing had happened, or I could 'rewind' and erase half the journey so that the group could experience the event before they reached their destination. I decided to ask for the opinion of the group. I let them decide whether to continue or go back. they opted to rewind the journey.
Many DMs would not have done what I did, they would have continued as if they had not made a mistake and continued to roll the adventure onward. I think that it is ok to improvise past mistakes if they have minimal impact to the game, but where there is a major error on your part the players should be informed. I realize it breaks the flow and immersion of the game, yet it is also important to be honest with your players. T Here needs to be mutual trust between the DM and the players. It is often necessary to get player opinions, and cater to their desires. There are multiple arguments that can be made for or against what I did in the above scenario, but I think it is important to admit your mistakes to the players and try to fix them as a group.
What mistakes have you made as a DM, and how did you rectify the situation?