This shyness makes it hard for me to speak in public, or even to go out with my friends as often as I should.

in 是介词，表示"在...之中"或"在...情况下"。 public 是名词，指"公众、公共场合"，来自拉丁语 publicus（人民的）。 in public 这个短语表示"在公共场合、公开地"，指在能被大众看到或听到的场合。