1 It doesn't sound familiar
When we hear our own recorded voice it sounds different than the sound we hear when we speak. Other factors such as the internal vibrations of our bones and skull alters the sound we hear when we speak.
2 It's actually a different sound
When we speak we don't just hear our voice through the waves that pass through our ears but our hearing also gets affected by the vibrations that happen in our bones as we speak. This makes the two sounds different from each other.
3 It's high pitched
When we speak the internal vibrations happening in our bodies make the voice sound deeper and low pitched. When we hear our recorded voice the voice will be less deep and of a higher pitch.
4 It sounds less masculine
When we hear our voices through a recording, which is the sound everyone else actually hears when we speak, we find it louder, thinner, higher pitched and less masculine. (See Why my voice isn’t deep?)
5 Recording equipment might be inaccurate
According to a Quora thread, the recording equipment we use might not be accurate enough to help us hear our own voices as they sound to others. Depending on the quality of equipment, our voice can sound much worse than it really is.
6 Your brain doesn't interfere
When you hear your own voice your brain usually interferes and gives you the impression that your voice is actually better. When you hear your own recorded voice the absence of this brain interaction can make you sound worse.
7 Your voice gets dampened
When we speak the tympanic membrane gets tightened and so the voice we hear gets dampened. When we hear our recorded voice it sounds very different than the voice we hear when we speak. (See How to have a deep voice?)
8 It doesn't match our mental image
People have a mental image of how they look and sound. When a person finds that his voice doesn't sound like the one in his mental image he gets disappointed.