In learning the deen, it is essential to have a teacher. but how about wordly knowledge?, Is it wrong to rely on autodidact when studying wordly knowledge?
All perfect praise be to Allah, The Lord of the Worlds. I testify that none is       worthy of worship except Allah and that Muhammad  is His slave and messenger.
  is His slave and messenger.        
In principle, the worldly sciences, just like other sciences, should learnt from a teacher (whether physically attending or online). In some fields, learning worldly sciences without a teacher could result in harming people. For example, if one learns engineering without a teacher and then builds a house, it could collapse on its inhabitants because he did not master engineering since and used the wrong method to obtain this knowledge. Likewise, if one learns medicine without a teacher, he can easily make a mistake in prescribing the medicine to patients, and thus harm people.
However, there are some worldly sciences which one can study without a teacher and no harm would result from that, such as programming, web design and so on; there is no harm if one learns such sciences on his/her own without a teacher.
For more benefit, please refer to Fatwa 166265.
Allah Knows best.
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