It's a different kind of thinking/doing compared to other specialties. You think and do at the same time, sometimes in critical, life threatening situations. Example - kid is intubated, becoming hypoxic, you are thinking about the differential (faulty connection, bronchospasm, R mainstem intubation, PTX, VAE, intracardiac shunt, etc.) and at the same time doing to rule things out (100% FiO2, check connections, listen to lungs, look at CO2 monitor, PIP, etc). Now if it takes you more than a few seconds to recognize the hypoxia and start to act, the kid's life could be in jeopardy and this hypoxia could progress to cardiac arrest. Not like on medicine rounds where you get lab tests, imaging studies, talk about the differential, consult some specialists, and then institute your treatment.
I have the utmost respect for internists. Their knowledge is vast, but our medicine colleagues just don't deal with critical situations daily. And that is the point - it's a different kind of thinking, a different differential (you have to know what could kill the kid the fastest and look for it), and a different mindset to fix the problem.