The elements of enjoyment, challenge/achievement and safety/flexibility are very important to the success of any trip. Equally important is the balance of these three. A trip which is very safe but has no satisfying achievements will be rather dull. Alternatively, a trip where all thought and energy is devoted to achieving some ambitious goal may be very risky.
You must strike an appropriate balance between the three areas of concern. The right balance for one group may be very different from that for another group or in other circumstances, and the balance may change during the trip. Flexibility can be learned and will be more easily applied if you have thought through all the options. Judgement will improve with experience.