In Surah Nahl, verse 43 we read:
“Ask those who know if you don’t know (something).”
let me give you an example:
What do you think an engineer would do if he got sick?
start spending so much time studying and doing lots of researches to figure out how he can get rid of the disease he's suffering from.
go to a doctor and ask the doctor to save him the trouble of all those exhausting effort.
A sane person will definitely choose the second way.
The above-mentioned verse is exactly implying an intellectual rule which is: "a non-expert person in a certain field has to go to an expert in that field."
Knowing that the skill of distinguishing between authentic Hadiths and the fake ones, understanding the correct meaning of the verses and traditions and reconciling between them when coming across a contradiction is not reachable without years and years of hard work, we can simply conclude that the only reasonable way of finding religious rules and regulations for non-expert people is following Islamic experts (Mujtahid) .