It means to stop action and not be able to move forward because of the constraints of one's own action or because of external influences. For example: after a day and night of rapid march, at this time everyone's physical strength has been seriously overdrawn and can not move forward.
Another example: seeing the water rushing down from the ravine, like ten thousand horses galloping, he was too scared to take a step. Inability to step may be due to their own physical reasons, or it may be hindered by external factors.
It means that the feet or legs cannot move. The reason for not walking is that there are obstacles in front of you, and then there are problems with your feet and legs. This phrase is used to mean that the work can not be done, or the ability to work is insufficient.
If you can't take a step, you can't make up your mind to leave. Because of the tangled heart, as well as paying too much, people have a great dependence or difficult to give up the emotion, so it is difficult to make a decision to leave who, can not step forward is not the determination.