The short answer to that question is: No, it is not hard to learn but it is hard to master! Calligraphy is a skill, that takes quite some practice in the beginning until you get the hang of it but you will need years and years of practice until you are a master at it. This is the case with most crafts though.
Can you teach yourself calligraphy?
Learning calligraphy is going to take a ton of practice. ... But calligraphy and lettering are specialized skills. And just like you wouldn't pick up an instrument and know how to play a song right away, you can't just pick up a brush pen and be a master at calligraphy or lettering. You need to practice.
How long does it take to learn calligraphy?
A few hours each week over the space of 2 months will equip anyone with the skills to write their own wedding stationery, gift tags or greetings cards. 2 months of regular practice will also tell if you have the natural talent to turn your calligraphy lettering into art. Every calligrapher has their own unique style.