Science is a collaborative effort. Very rarely does a project ever get done by one person without the valuable input of others. Increasingly, funding agencies are looking to put money toward interdisciplinary research, on both large and small scales. Even universities are increasingly moving to shared space for research labs.
As a PI these waters can be a little tricky to navigate, but as a trainee they can become downright treacherous. Set aside the issues of 4 equal first authors for a second and think about the way we talk about science. At least in my field, it is extremely common for lab members to use "we" when discussing lab research. In many cases that is entirely valid - the full story is often a compilation effort. But there are exceptions.
One of the most critical time for a early-career scientist to say "I" is for job interviews. Interviewing for a postdoc, faculty or industry job? It's time to break out the I. Concerned about seeming selfish? Don't be. What is critical to get across during an interview is all the great things YOU did. Having the context of the lab's work is important, but do not leave what you did vs. what lab technician or the other postdoc did, remain ambiguous. Sell yourself for what you have contributed, while openly acknowledging the efforts of others.
This is what your interviewers want to see from you. Don't make them try and read between the lines.