In most circumstances, telling a person to be "realistic" is one of the most stupidest, useless pieces of advice out there.
Of course, for upper middle class jobs you need need certain allocations to ensure you are viable, such as being a lawyer, doctor, engineer, pharmacist, IT worker. Furthermore, bullshit jobs like twitchers, content influencers like Brooke Monk, Kayla Mae Smith, Andrew Tate, Rosie McClelland, etc you need to be discouraged as they are just simply a waste of time.
Otherwise, telling someone to be realistic is stupid and actually backfires them from their desired goals. This is owing to the fact that it forces labelling and self-fulfilling prophecy, in which someone may be predicted to fail and ultimately fail owing to that in-grained, internalized third-party factor. For example, Sajid Javid was blocked from doing O-Level (now GCSE) Maths and had to only do one A-Level because he needed to stay in his lane, career advisor said that he can only be a TV repairman. Further, my lovely fellow A-Level Sociology teacher was discouraged by her A-level English Lit teacher from applying to university in 2009 (when she was in Y13/12th grade) because she was presumed to fail. These advice are useless and stupid.
One of my desired careers is to be a social worker or a chartered accountant, and I was told by someone to be "realistic" because these have tech stuff in it, or that because of my ethnicity, there was an assumption that I have an immigrant or a mixed accent when I have a nearly received prounounced Southern one, therefore me being a social worker for youth and child protection is seen as not viable. What on Earth? I study Politics A-Level along with Business and Sociology so the knowledge and analysis as well as passion is there, so I should be viable.
Unless if they are based on jobs like science stuff, people who tell you to be "realistic" are nonsensical, dorky people with no motivations themselves and are jealous of your ambitions because you have the skills that they do not bother having.
Stay away from anyone who says this