And when is it time to complain about load and when are you lazy?
Has anyone encountered such issue?
Never.
Complaining is a waste of your time and efforts. You are not original enough to come up with a new complaint, so don't bother.
When my boss wants to add to my workload, I sum up what I am currently working on (no more than 2 sentences here) and ask where the new work falls in priority.
Remember, you should always have work to do, there is no "done". You are there to exchange your time and expertise for money. Complaining simply puts pressure for a lower exchange rate.
As for office politics, this is the primary driver of employee dissatisfaction.
1. You get a job, you are happy, new opportunity, etc.
2. You get familiar with tasks and coworkers.
3. You get caught up in office drama. Turning your attention away from your goals and achievements, and toward your co-workers and maneuvers. To misuse a line about academia, "The office politics are so viscous, because the stakes are so low". Most of the competitors are competing for social positioning, rather than advancement. Lines about pig wrestling come to mind.
Rather, focus on achieving competency, which should take 40-60% of your attention, and a few weeks or months. Then keep your eye on the prize, which is to not need to come into that office again.