Some of this might just be genetic. Some of this might also be due to fear periods. According to most behavioral literature puppies go through two, the first at some time between 8-11 weeks and the second some time between 6-14 months. (I'm convinced one of mine actually went through three periods, as he got very jittery at around 9 months and again at a bit over a year.)
During a fear period a puppy is nervous around things that wouldn't previously have bothered him. Even worse, he can develop an outsized fear of something that startles him during this period, so he remains nervous around that thing forever. One of my dogs was permanently afraid of big blue US postal service mailboxes because I was careless about posting a letter during his second fear period. As we were walking past the mailbox I casually lifted the flap (which opened with a rusty screeching sound), dropped my letter in, and let the flap drop again with a great echoing boom. My startled dog shot forward in a panic and refused to come within six feet of a mailbox for the rest of his life.
Unfortunately, this was in the time period where dominance training theory was at its peak. With well meaning ineptitude I made the problem worse, because I insisted on walking him past the same mailbox every day. I thought I could get him used to it by repeated exposure. Instead, by dragging him past the mailbox, I simply made him so scared that he learned to slip his collar and run home. Knowing what I know now, I will forever regret mishandling his nervousness.
There was an earlier thread in which someone discussed problems they were having with their puppy, which was afraid of car rides and also leaving their yard. You might find some of the training ideas helpful. Fear of the outside
During a fear period a puppy is nervous around things that wouldn't previously have bothered him. Even worse, he can develop an outsized fear of something that startles him during this period, so he remains nervous around that thing forever. One of my dogs was permanently afraid of big blue US postal service mailboxes because I was careless about posting a letter during his second fear period. As we were walking past the mailbox I casually lifted the flap (which opened with a rusty screeching sound), dropped my letter in, and let the flap drop again with a great echoing boom. My startled dog shot forward in a panic and refused to come within six feet of a mailbox for the rest of his life.
Unfortunately, this was in the time period where dominance training theory was at its peak. With well meaning ineptitude I made the problem worse, because I insisted on walking him past the same mailbox every day. I thought I could get him used to it by repeated exposure. Instead, by dragging him past the mailbox, I simply made him so scared that he learned to slip his collar and run home. Knowing what I know now, I will forever regret mishandling his nervousness.
There was an earlier thread in which someone discussed problems they were having with their puppy, which was afraid of car rides and also leaving their yard. You might find some of the training ideas helpful. Fear of the outside
