There are multiple reasons to support how Walton and Victor Frankenstein are similar in personality (as seen in Mary Shelley's novel Frankenstein).
By far the most chilling quote from the novel that shows the similarities between Victor and Walton is Victor's accusation. Victor accuses Walton of being mad.
“Are you mad, my friend?” said he; “or whither does your senseless curiosity lead you? Would you also create for yourself and the world a demoniacal enemy? Peace, peace! learn my miseries, and do not seek to increase your own.” (Victor--Chapter 24)
Here, Victor is simplistically "calling the kettle black." Victor has certainly gone mad, driven by his obsession with finding his monster. Victor is a man compelled by his own desires--even to his demise. Concerned that Walton is much like himself, Victor tries to reason with Walton, to convince him to reconsider his actions.
Another passage which shows the similarities between Walton and Victor is seen in the letters from Walton to his sister. The opening lines of his first letter are as follows:
You will rejoice to hear that no disaster has accompanied the commencement of an enterprise which you have regarded with such evil forebodings. I arrived here yesterday; and my first task is to assure my dear sister of my welfare, and increasing confidence in the success of my undertaking.
Here, after reading the text, one can see that the families of both Walton and Victor have shown concern for the "enterprises" which they seek. Walton, like Victor, refuses to accept the concerns of his family regarding his "voyage." Victor, also, fails to listen to his family and their concerns.
In the end, both men are simply too driven by their own passions to regard the warnings of others.
Both Walton and Frankenstein have a desire to endeavour the unknown.
They are both alien in their society- both of them being socially isolated in the way that they both seclude themselves from society and confine themselves almost alone.
They both eventually understand the dangers of knowledge.