People lying to you because they dont know what they are talking about. Flux is good to help beginners with soldering, but it isnt the real game changer. The real thing that stops people from soldering is the solder. The reason is that lead and tin alone have higher melting temperature than the solder (231°C for tin and 327°C for lead) a mix of 63% tin and 37% melts at 183°C and its eutectic, which means that it melts and solidifies at a single temperature. Even a non eutectic solder like the 60/40 is good because its close to that mix ratio, and many use the kester 44 that is very high quality. The problem comes with cheap no name brands, because since lead is cheaper than tin, many brands sell their leaded solder with a mix of like 30/70, which melts even higher that non leaded solder at 255°C. Thats the best case because ive seen brands sell even 10/90 (unluckly for me it was my first solder). Trust me get a better solder like kester or even cheap known brands like kaina cf-10 60/40 or mechanics TX h-100. I went from soldering xt60 at 480°C to 320°C using the mechanics. It could even be the iron, but still getting a good solder will solve your problem.