On a map, the path between Namche Bazaar and Tengboche does look like a relatively easy walk. By the end of the day, the difference in altitude between the two villages is just a small climb of 500 meters. Unfortunately, this is just half of the truth: After a steep climb out of the Namche Bazaar village, the trail levels out. It then descends slowly from 3500m to 3200m, before ending in a steep climb of about 700m.
Asking other backpackers on the route, which part of the Everest Base Camp trek they think is the hardest, most of them will point out the stretch between Monju and Namche Bazaar. As we did stay overnight in Phakding, it took us about 90 Minutes to get to Monju first, where we had a small rest before the steep ascent.