  One well-tested method in science is to separate the object of interest from
its surroundings and look at it in isolation. The advantage is that unimportant
information is removed and the true properties of the object are seen more
clearly. However, sometimes the influences of the surroundings actually
determine the properties of an object. In this case, not taking the environment
into account can lead to incomplete or even false conclusions. In the context
of planet formation this question arises to: is it sufficient to study the
nascent planetary system in isolation? Stars usually do not form in isolation
but as part of a stellar group. The first important question in this field is
then: How important is the influence of the surrounding stars on circumstellar
discs and forming planetary systems?} We can also pose a second question: Does
radiation or gravitational interaction dominate? Here I give my perspective on
these two questions.
