Pilots have forgotten to raise the gear after take off and when they realise it, they instantly go for the undercarriage lever without first checking speed. Normally 250 kts is the climb speed and whilst the aircraft can be flown gear down at this speed, its 30 kts above reatraction limit. If you ever find yourself in this situation, overcome the knee jerk reaction to raise the gear and pull speed, slow down and then retract. You will probably get a call from the safety department as retraction height is monitored but at least you won't damage anything.