The practical part of the translation practice, practically begins when a text is read/heard by the translator/interpreter. He/she, then, starts comprehending it, during which each translator/interpreter takes it in his/her own more or less unique way, i.e. there is a mysterious "black box" in him/her which determines which aspect of the text is more prominent, which part plays a more important role in the overall conveyance of the message involved, which word(s) carry a stronger sense etc.
Once the text (or a part of it) is transmitted into the "black box", then a sort of "piece of knowledge" is formed within that mysterious "black box". We have already presupposed that the "box" exist within the mind of the translator/interpreter; so, implicitly he/she is able to put that piece of knowledge into a new form called "the target language text". His/her success crucially (if not totally) depends on two factors:

Both of these factors are somehow characteristics of the same mysterious "black box". There is also an element of creativity involved in, but its role is much less considerable than, let's say in writing.
That is the time, when the "box" (about inside of which we know almost nothing) starts "emanating" the new text.
Again, here each individual translator/interpreter has his/her own more or less unique "black-box" characteristics, determining which aspect to sacrifice, e.g. form over content or vice versa, which part to emphasize on etc.

Conclusion

To contribute to the natural process of evolution of a quality translator/interpreter, we should "help" the box in some ways: