Como no seas más realista, te vas a frustrar cuando las cosas no salgan perfectas.

If you are not more realistic, you are going to get frustrated when things do not turn out perfect.

Breakdown of Como no seas más realista, te vas a frustrar cuando las cosas no salgan perfectas.

• ser: to be
• tú: you
• cuando: when
• ir: to go

Questions & Answers about Como no seas más realista, te vas a frustrar cuando las cosas no salgan perfectas.

What does Como no mean at the start of this sentence?

Here Como no means if you don’t or unless in a warning-like sense.

So:

• Como no seas más realista... = If you aren’t more realistic...
• It does not mean as or since here.

This structure is very common in Spanish when someone is giving a warning, caution, or mild threat about what will happen next.

Why is it seas and not eres?

Because after Como no used as a warning, Spanish normally uses the present subjunctive.

• seas = subjunctive of ser
• eres = indicative of ser

So:

• Como no seas más realista... sounds natural for a warning.
• Como no eres más realista... would be wrong here.

This is one of those patterns you learn as a chunk:

• Como no + subjunctive, ...

Could I say Si no eres más realista instead?

Yes, you could say Si no eres más realista, te vas a frustrar...

That version is grammatical, but the tone is a bit different:

• Si no eres... = more neutral, plain condition
• Como no seas... = stronger, more like a warning or caution

So Como no seas... feels a bit more emphatic, especially in spoken Spanish.