i learnt that Imam Bukhari (ra) took only 3,000 hadiths frm 600,000.
is it true? does that mean we are unaware of much hadith?
assalam 'alaikum warahmatullahi wabarakatuh
Sahih al-Bukhari contains only Sahih hadiths.
Sahih Muslim contains both Sahih and Hasan hadiths.
Other books such as Sunan Abu Dawood, Sunan at-Tirmidi etc contains Saheeh, Hassan and Da'eef Hadiths also. But all of them are very clearly explained and separated alhamdhulillah.
Imam Bukhari (may Allah have mercy upon him) said that he did not write a single hadith in his book before performing two rak'ahs, and make du'a. MashaAllah!
I am not sure about those values, but I am sure that he did not write many hadith which he was not 100% sure to be Sahih, in his book. That is the reason 'Sahih al-Bukhari' is considered as the second Holiest Book on the earth today, from the Ijma' of 'Ulama.
No brother we are not unaware (here WE means 'Ulama of the Ummah) of many hadiths. This is a huge part of 'Ilm in Islam.
Hope it helped a little.
wassalam 'alaikum warahmatullahi wabarakatuh