Why didn't Simran get into bogey from first door in DDLJ?

As noted, this is only speculation, but the woman is not running to catch a train, she is running to a man who looks to be waiting to help her aboard. Logically, she could have taken the first door, but if this is a romance, it would not be the romantic choice. I don't think this is an accident by the film-maker, but a confirmation of her intent and the intent of the film.

Personally I believe it is an unintentional error by the director. Now the viewers observes a lot more than a director thinks. But if I am to cover the director I would say, it really depends upon the way a person thinks. Generally ladies are said to like taking decision by heart rather than by brain and it is true. May be if this was SRK in place of Kajol as the runner, he might have entered by the last gate! I feel at that particular moment Simran was so eager to meet Raj in that situation, she did not think about it.

But if I see it logically, it is a foolish mistake by the makers. They should have made him stand in the last door of the bogey.

This is not an unintentional error by the makers of the film. There might be two reasons for this scene.

1. Here Simran's destination is not the train but Raj. By this scene, he wanted to show how desperate the love between the actor and actress. She didn't look at other ways. Only thing she could see is Raj his love. This is what the director and writer wanted to convey to the audience. One of the producers and writers of this movie is Late Yash Chopra. He is called the King of Romance. He is renowned as the director who taught Romance and unconditional love to Bollywood. So we can't ignore his part in filming this episode.

2. The velocity factor: It is difficult to board a moving train. We can board a moving train with some help. Since Raj is stretching his hand to help Simran boarding train, she is running towards him help to board the train.

Who thinks that the director is mistaken is foolish or stupid? He wanted to show how the romance looks like. The scene came earlier in the movie when they were strangers and later when they are lovers. If she entered from the first gate the movie would have lost its eternality and a scene repeated more than 100 times and one of the best ending with the best music. It would have been dry, dull and free from romance.