The Bernoulli's principle states that the quantity p+ pgz + pv[superscript 2]/2 must be conserved in a streamtube if some conditions are matched, namely: steady and irrotational flow of an inviscid and incompressible fluid. In most physics textbooks this result is demonstrated invoking the energy conservation of a fluid material volume at two different positions of a pipe whose cross-section and height vary along its way. Although the final result is correct the right justifications presented in textbooks are usually unclear or absent. The main problem rests on the work done by pressure, which are not found to be fully justified via free-body diagrams as depicted in many general physics textbooks, not to mention plenty of videos on YouTube that incur in similar omissions. In this article I will discuss this issue and how it is solved without resorting to alternative demonstrations. In addition, I discuss the needs of the assumptions to get the Bernoulli's principle in a way viable to introductory physics courses.