With regards to the student of knowledge being thoughtful and not one who is hasty in speech and action, the Shaykh Muhammad ibn Saalih al ‘Uthaymeen rahimahullaah comments:
What is important is ta-ammul (being someone who contemplates) – meaning being patient and biding one’s time, and that you do not speak until you know what you are saying and what the result (of it) will be.
And therefore they say, “Do not place your foot down except (somewhere) that you know of safety (for it).”
Meaning a person walks and he does not put his foot upon anything about which he does not know whether it is a hole or a thorn or a pebble or ice – until he know where (for certain) he is putting his foot.
So this type of ta-ammul is of great importance. And do not be hasty unless there is a necessity which calls you to that…
Therefore, the issue lies between (two aspects) – do I bide my time and remain patient – or do I act with haste and lead the way?
Which of the two is to be given precedence?
The first is – because a word and an action cannot be taken back once they have come out from you. However, as long as you have not spoken or done an action, then you are still free.
So reflect on what you are saying and what will be the benefit – the benefit of (your) speech?
And, therefore, the Prophet sall Allaahu ‘alaihi wa sallam said:
Whoever believes in Allaah and in the Last Day, then let him speak good or remain silent. 
(Sharh hilyah taalib il ‘ilm p51 to 52 of Shaykh Muhammad ibn Saalih al ‘Uthaymeen rahimahullaah. Translator Nasser ibn Najam)
 Reported by al Bukhaaree (5672), Muslim and others