With regards to the student of knowledge having the least excuse for not acting upon his knowledge, Shaykh Muhammad ibn Saalih al ‘Uthaymeen rahimahullaah comments :
So what is the fruit of knowledge?
The fruit of knowledge is: acting upon it and calling to it.
Therefore the obligation to act upon knowledge for the student of knowledge is greater than what is obligatory on other than him – because the ignorant person is not an imaam (leader). So he is not taken as a role model, not in his action nor in his statements.
However the student of knowledge is taken as a role model. Therefore, upon the student of knowledge is to act on his knowledge because the student of knowledge carries his weapon – either it will be against him or it will be for him, just as the Prophet sall Allaahu ‘alaihi wa sallam said:
The Qur-aan is a proof for you or against you. 
And there is no third category here, such that the Qur-aan would be neither for you nor against you. It is either for you or against you, so when will it be for you?
The answer: It will be for you if you act upon it, and if you are a righteous role model in directing the creation towards goodness.
And it will be against you if you neglect it and turn away from it and relinquish it.
Therefore it is obligatory upon us to act upon knowledge and that we be righteous role models and that we be imaams for our Islamic nations in whichever place (we are in) – because if a person acts upon what he knows, he becomes an imaam; Allaah, the Most High, will bequeath to him knowledge which he did not know of before.
Pay attention to this point: if you act upon what you know you will become an imaam and the people will copy you and you will become a role model, then Allaah, the Most High, will increase you in knowledge and he will bequeath to you knowledge of a matter which you did not know beforehand.
And read the statement of Allaah, the Most High:
And as for those who accept guidance, then He increases them in guidance…
Meaning: in knowledge.
…and He bestows upon them their taqwaa (fear and dutifulness to Him).
Upon you is action on knowledge.
If you know that Allaah has made obligatory such-and-such upon you, then hasten to (do) it. You know that Allaah has made such-and-such forbidden for you, then distance yourself from it.
And if not, then you have missed out on the fruit of knowledge, you have completely missed out on it.
Therefore the fruit of knowledge and the intent behind it is acting (upon it).
Quoted in Wasaayaa wa tawjeehaat li tullaab il ‘ilm pages 258 to 260, translated by Nasser ibn Najam