Sala'am Doaa The form 'overcoming ' is correct, and the reason for this has nothing to do with the word 'to'. If you think about the phrase 'the key to the door' , the phrase 'key to' is followed by a noun phrase: 'the door'. And even when you are using the word 'key' in a figurative sense, the word 'to' still needs to be followed by a noun phrase. In your sentence above you have a long noun phrase, starting with a verb. And how do you make a verb do the job of a noun? You add 'ing'. This form is called a gerund, and verbs usually take this form when they are the subject or object of a sentence. 'overcoming' is does the job of a noun in this phrase, in the same way as 'door' is a noun in the example above. I hope that's clear.

Don't always assume "to" is part of an infinitive verb. Whenever you aren't sure if you need an infinitive or a gerund, take out the verb and replace it with a noun. If it makes sense with a noun, then you use a gerund. You never use an infinitive in this context. The key to the door. The key to success. The key to overcoming bad habits. You would never say "the key to overcome", as that means "the key that I must overcome". Yet we don't overcome keys. We overcome obstacles. :) Also (because this is another common stumbling-block for learners)... I'm looking forward to your reply. I'm looking forward to tomorrow. I'm looking forward to seeing you. ("I'm looking forward to see you" has a different meaning, and sounds unnatural anyway.)